Plastic blow molding of containers is conventionally performed either by extrusion of a hot plastic parison or by a plastic preform which is usually injection molded from plastic. The hot plastic parison or heated preform is received within a mold cavity whereupon pressurized gas provides the blow molding of the container to the shape of the mold cavity.
With certain resins such as polyethylene terephthalate, the resin has to be treated to increase its intrinsic viscosity in order to have sufficient strength to be extruded as a hot parison capable of being blow molded, such as disclosed by U.S. Pat. No. 4,219,527 Etelman et al. Such processing of the resin increases its cost and hence the resultant cost to the consumer.
While preforms for plastic blow molding are conventionally injection molded from a single resin, there have also been prior multi-layer preforms such as disclosed by U.S. Pat. Nos. 3,719,735 Valyi; 3,787,157 Valyi; 4,067,944 Valyi; 4,391,861 Nilsson; and 4,646,925 Nohara.
Other prior art involving plastic resins, parison extrusion and preforms is disclosed by U.S. Pat. Nos. 4,398,642 Okudaira et al.; 4,564,541 Taira et al.; 4,728,549 Shimizu et al.; 4,764,403 Ajmera; 4,816,308 Shimizu et al.; 4,861,630 Mihalich; 4,874,647 Yatsu et al.; 4,994,313 Shimizu et al.; 5,034,177 Niimi et al.; 5,039,780 Hashimoto et al.; 5,115,047 Hashimoto et al.; 5,256,363 Hashimoto et al.; 5,281,387 Collette et al.; 5,286,187 Niimi et al.; 5,380,479 Schrenk et al.; and 5,439,718 Klerks et al.